Window Installation in Ireland — Cavity Closer, Dpc, and the Airtightness Detail
On this page
Window installation matters as much as the window. Cavity closer, dpc, expanding foam, and a continuous airtightness tape.
Window installation in Ireland: cavity closer (a plastic or insulated strip that closes the cavity at the reveal), dpc (damp-proof course, a horizontal barrier at the bottom of the reveal to stop water tracking in), expanding foam around the frame (to fill the gap between the frame and the wall), and a continuous airtightness tape at the reveal (a flexible membrane sealed to the wall airtightness layer and the window frame). The reveal detail is the most under-detailed part of most self-builds. A 1 mm gap in the tape is the equivalent of a 50 mm hole in the wall. Get the joiner and the airtightness contractor on the same page. Most airtightness failures are at window reveals, not at the window itself. Building Regulations 2023 TGD-L (Conservation of fuel and energy) governs.
When this matters most
You're at design stage and need to detail the window installation.
When this doesn't apply
The windows are in.
Sources
Building Regulations 2023, TGD-L. https://www.gov.ie/
Frequently asked questions
What is a cavity closer?
A plastic or insulated strip that closes the cavity at the window reveal. Prevents cold bridging and water ingress. Required at every window and door opening in a cavity wall.
What is the most common window installation mistake?
Missing or damaged airtightness tape at the reveal. The window is fine; the gap between the window and the wall is the failure point. A continuous tape sealed to the wall airtightness layer and the window frame is the answer.
Who installs windows in Ireland?
A window supplier usually does the installation, or a joiner. For Passive House or BER A1, an airtightness contractor may do the tape detail. Spec the responsibility in the contract.
When this matters most
You're at design stage and need to detail the window installation.
When this doesn't apply
The windows are in.
Where to go next
Next decision
The next step in your build sequence.
- Door Budget for a Self-Build in Ireland — Internal Doors, External Doors, and Ironmongery →
- Front Door in Ireland — Composite, Timber, Aluminium, and What the BER Counts →
- Garage Door in Ireland — Sectional, Roller, or Up-and-Over, and What the BER Counts →
- Passive House Windows in Ireland — U-value, Frame, and What the Certifier Wants →
- Sliding Doors in Ireland — Aluminium Sliders, Lift-and-Slide, and the U-value Trade-Off →
- Window Energy Rating in Ireland — What the Label Means and Why It Matters for BER →
Branch into
Adjacent decisions at the same stage.
Watch out for
Common mistakes, hidden costs, gotchas.
Compare with
Alternative approaches worth knowing.